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2 Person Bridge New Model

This is my continuation on the quest for the optimal two person bridge hammock. I have posted about my previous double hammock in this thread. My current double hammock version attempts to address some of the weaknesses of the previous design.

Strength: I had a seam rip out in the foot of my previous double hammock. This was after a night where the pitch was too low at the foot end. The weight of both people were pressed against the foot of the fabric as we gradually slid down towards the foot during the night. The seam was joining a folded corner of fabric back on to itself to create a corner of the footbox. Although it bummed me out at the time, it did not affect the lay of the hammock very much. What it revealed was my original sewing job was shoddy. A single row rather than a double row of stitching had been used. I didn't properly reinforce with grosgrain ribbon the edges of the footbox that were below the spreader attachments. Fortunately for me, my sewing skills have improved a lot in the nearly two years since starting that project. Sturdiness and durability have been given priority in the current model over weight saving ideas. The new hammock is reinforced with grosgrain just about everywhere.

Center Division: To keep the two occupants from continuously rolling into one another, I am using a central support rope to lift the center of the hammock. In the previous version it was basically good, but presented the following problem.
I noticed in my previous double hammock that the weight of the occupants seemed to be squeezing the pads towards the outside edges, leaving a strip in the middle without any real padding that created a cold spot. Where the pad compartments met, the central support rope pulled the top and bottom fabric layers together too tightly. The pads could not stay all the way inflated in between the hammock layers the way the fabric was being pulled up with the occupant weight pushing down. And so they were not meeting flush in the middle. BTW Rushthezeppelin anticipated this problem in my previous thread. I didn't see this as a problem before, but testing has proved him right.
To remedy that, I constructed a separate piece for the arc. In my current version, I used heavy nylon mesh that curves from about 1" above the bottom fabric in the center of the hammock to about 3" above at the shoulder. From there, the rope is not encased in the arc and rises more steeply to meet the inside ends of the head spreaders. In the opposite direction, it curves from 1" above in the center to about 5" above the hammock bottom fabric at the knees. from here the rope is no longer encased in the nylon mesh arc, and rises more steeply to reach the foot triangle apex. Before the central support rope pulled the fabric up, which created the arc, now the prefabricated arc allows the hammock bed to stay flatter.
This attaches at the apex of the foot end triangle and at the inside ends
of the two head spreaders. Double_net_down.JPGThe inside of the hammock is 1.1 nylon. which forms two pad sleeves. The inside lining is permanently attached at the lateral edges and an inch up the sides of the central arc made from the heavy nylon mesh.

Insulation: This current model is designed with a pad sleeve to be used with 3/4 length or full length inflatable foam pads. And while the 3/4 length pad is thicker and warmer under the torso, I like the full length better. The full length makes a more consistently flat hammock bottom. And I like the puffy rails that are built into the Pacific Outdoor Equipment Insul-Mat. They give sensory feedback whether you are centered on the pad, or whether you are laying partly off the pad. Without the sensory feedback from the puffy rails, I would need to wait for a portion of my body to become colder before I knew that I was partly off the pad.
In addition to the pad sleeve for the inflatable foam pads, there is permanent insulation that has been sewn in to the double hammock. From the foot section up to the waist two layers of insultex are sandwiched between 1.1 ripstop nylon.double_footend_empty.JPG
Also two side panels were created along the outside edges of the two foam pads and extend up in width to the lateral arcs of the hammock. double_pad_sleeves.JPGThey contain two layers of Insultex. In between the 2 Insultex layers is a section of 3/8" permanently installed closed cel foam also. It ranges from about 4" to 6" wide, and extends from the shoulder to just above the knees. It slightly overlaps the coverage of the inflatable pads while keeping them positioned flush with the center support of the hammock. The use of closed cel permanently installed foam pads in those side sections may have been poor judgment on my part. While it keeps things simpler for setup and take down having side insulation built in, it sure increases the bulk. And I am not sure if I really needed it. I am currently using a JRB compression stuffsack to pack the hammock away. The packed size is closer to triple rather than double the size of one of my single person bridge hammocks. In addition to the insulation, a large bugnet has contributed to the bulk also.

Bug Protection: A full bugnet enclosure is permanently attached.double_sideview_tarp.JPG Two 100" long zippers create doorways on each side. The bugnet can be fully retracted when bugs are not an issue. In this case, a toggle and loop sewn in near the feet keep the rolled bugnet contained and out of the way.Double_net_down.JPG

Storage: I installed two end caps at the head end of the hammock which separate storage areas from living space. Beyond the endcaps, I sewed two pockets nestled into the suspension triangles. The lateral side of each end cap was left unattached in order to reach a hand through it. head_pockets.JPGElastic webbing picks up the slack on the unattached edge and assists in keeping the contents in the storage pockets. They are big enough to put any daytime clothing at arms reach while laying in the hammock. These were troublesome to make. I didn't anticipate the head spreader angles correctly when I made the pockets. I added a panel onto each pocket to correct the mistake.

Foot Print: The measurement between the outside tips of the two head spreader bars are 54" in width. This is a full 10" narrower than my previous model. No doubt this will help with site selections for setting up the hammock. Even more importantly, it allows a steeper pitch of the tarp.double_heac_end_tarp_bugnet.JPG During a night on the Arizona Spring Hang, the tarp of my previous model collapsed from the weight of snow. I just shook off the tarp, reset a stake, and climbed back in the hammock with little damage done. Still, I knew that the wide pitch of the tarp was the biggest contributing factor that led to that problem, so I made a strong mental note to address it with my current double hammock design. I'm happy with the current dimensions.

Hanging between 2 trees rather than 3: Oh, I wish I could have gotten this to work. This is how I attempted it and failed. I added a 44" ski pole to the setup. The head end tree strap formed a suspension triangle from the tree to the ski pole. My two head suspension triangles at the top of my hammock were attached to the two ski pole ends. So basically. it was a primary suspension triangle which branched into two secondary suspension triangles.
This was already getting complicated, and was not yet supportive enough to securely hold a single occupant without extreme tilting. Yet, I stubbornly persisted. I tried tying a second strap near the base of the tree at the head end, with two ropes leading from it. The two ropes from the strap attached to the two ends of the pole tips. I hoped it would fix the extreme tilting. It did partially accomplishing that, but still not good enough. I thought I was on the right track, but it still tipped too much for my liking with only one person in it. So I tied a third strap, again with two ropes leading to the end of the ski poles. This strap was positioned two feet above the primary head end treestrap. Now this thing was starting to resemble a weird kite or bizarre art form. I actually had four sets of ropes converging at the ends of that ski pole! My primary suspension triangle, one that originated at the base of the tree, one that originated higher in the tree, and finally the secondary suspension triangles that are built into the head end of the hammock.
Hanging it this way had the effect of "pre-tensioning" the hammock, which then sunk less when the occupants climbed in. I thought, "maybe this is good", but I was so wrong. I got my girlfriend to try it out with me, but it promptly broke ski pole just as soon as we put our combined weight in it. I then found out the ski pole had only been loaned, not given to me. So that item now goes to the top of my gear wish list- bummer. I'm sure the mathematically gifted hammock designers would have for seen the excessive compression forces that this arrangement produced. But I didn't see it, except through hindsight.
So I'm back to hanging it between three trees. The separation of the head attachment points is best at around 5' (it can be as little as 4'). At over 10' of separation the treestraps had to be placed very high, at least eye level to keep the hammock from brushing the ground when occupied. I really prefer to have equal distance between these head attachments. If not, then I lay on the side with the shorter length, since I am heavier and otherwise make the hammock sink a little lower on my side. If the third attachment point at the feet is not exactly centered between the head attachments, I use a spare length of rope to try to pull one of the attachment points in such a way to achieve symmetry. In summary, the setting up of the double hammock presents more of a challenge and takes more time than setting up a normal hammock that has the usual two points of attachment. I guess that is to be expected, but I still think I should be able to find ways to simplify and improve this aspect of double hammock use. I'm sure with practice, I will at least get faster at it.

Reactions: I got some excellent unsolicited responses from my girlfriend about sleeping in this hammock. Her feet were really warm (remember I put two layers of Insultex from foot to waist). She also said, "My back felt great!" And " It was SO comfortable!"
Her criticism was that we can't really hug in it. A little experimenting proved that it was not really true. Yet, the criticism is valid when compared to the ease one has in their own bed. The problem has to do with the way the center support rope lifts up as it exits the head end of the hammock to reach the inner corners of the head suspension triangles. It is performing an important function, but it also gets in the way. This is a design aspect that still needs some work.

Dutch and Grizz. You guys are right, the challenges never stop. There will still be lots of room for improvement. Meanwhile the incremental steps on the way are pretty enjoyable.

Drewboy, thanks, and good idea about making the Arizona Spring Hang an annual event. It was loads of fun!

Thanks, Headchange4u, but I think I still have plenty of changes in design yet before this project is finished. For instance; just how independent should each side of the hammock be? If each side is more independantly suspended, the occupants won't be able to hug easily. If less independent, there will be more disruption when one exits the hammock and one remains. These thoughts will factor in to the design of my central support rope. I'd really like to find a solution to this and it will mean a significant redesign of the head-end suspension.

Otherwise, if you want to get started on one right away, here is the basic premise. You take two bridge hammock patterns and splice them together. Where the feet intersect make it just a little bit less than 50% overlap, at the top make the intersection a little bit less than 10% overlap. So these two bridge patterns now form a double bridge pattern. So that's it in a nut shell.

Revisions

...I think I still have plenty of changes in design yet before this project is finished. For instance; just how independent should each side of the hammock be? If each side is more independantly suspended, the occupants won't be able to hug easily. If less independent, there will be more disruption when one exits the hammock and one remains. These thoughts will factor in to the design of my central support rope. I'd really like to find a solution to this and it will mean a significant redesign of the head-end suspension.

So far employing this strategy has required the two head end suspension points to be strung more tightly. As we know this puts more stress on the entire suspension, and is what contributed to a Metolious crash buckle failure (the hook snapped off at the bend in the metal). But this approach also drops over 7 ounces from the hammock weight by leaving out the head end spreaders, and I will continue to experiment with it.